This invention relates to a static random access memory of a volatile type, which is suitable for use especially in portable electronic devices where power supply is limited.
In a conventional static random access memory (RAM), a power source, which is connected to a memory cell array constituted from a plurality of memory cells, supplies an electric current of a specified amount to the memory cell array at all times. The current is supplied not only when the RAM is in an active state where reading or writing of data in the memory cells is carried out, but also when the RAM is in a stand-by state wherein data in the memory cells are held without any change.
Generally, in static RAMs, an electric current necessary for the holding of data in a memory cell is smaller than the electric current necessary for reading or writing of data in the memory cell.
In the above conventional static RAM, however, the electric current is used as much in the stand-by state as in the active state, as stated above. In other words, the conventional RAM wastes electricity. Therefore, if the conventional RAM is used in an electronic device such as a portable device where a power source has a limited life or capacity, it is very difficult to hold data for a long time.